Disk and Tape Storage Cost Models

1. Disk and Tape Storage Cost Models Richard Moore & David Minor San Diego Supercomputer Center (SDSC) University of California San Diego Presented to: Designing Storage Architectures Meeting September 17-18, 2007

2. Objectives & Outline • Realistic cost estimates and projections are critical for storage users/providers • While much info is available on vendor hardware solutions … • Little info on integrated costs from storage provider perspective • Estimate costs for at-scale provider to ‘store bits’ • Outline • Caveats • SDSC’s Storage Infrastructure • ‘Bit Storage’ Cost Estimates • Tape Archival Storage • Disk Storage • Projections – with scale of storage facility and into the future • Conclusions

3. Caveats on Cost Estimates • Sustainable storage • Annual cost w/ media/technology refresh & data migration • Not write-once and put on a shelf • Based on SDSC experience only • Include UCSD’s indirect costs – will vary by institution • Other providers may have different cost structure • Based on SATA disk and enterprise-class tape systems • Cannot be specific about vendor costs or burdening, but relative fractions are reasonable • This is a snapshot as of Jan 2007 - will decline w/ time • Paper focuses only on single-copy ‘bit storage’ costs ‘Bit storage’ is only a fraction of the cost to ‘preserve data’

4. A Three-Stage Model for A Digital Preservation Environment Use Ingest Store • Replication • Geographically distributed • System diversity • Verification & recovery • Synchronization • ‘Master’ version • Propagating to replicas • Audit trails • Mitigation of termination risk • ‘Bit Storage’ • Capacity • Online (disk) • Archival (tape) • Single-copy reliability • Media/technology • advances • Data migration

5. SDSC’s Storage Infrastructure

6. SDSC’s archive shows exponential growth w/ a consistent doubling period of ~15 months

7. Cost Elements of Bit Storage Estimates • SDSC’s Cost Estimates Include: • Annualized capital costs of the media (including disk controllers) • Other annualized capital costs • Disk: File system servers, SAN gear • Archive: Silos, tape drives, disk cache, file system servers • Hardware maintenance and software licenses (annual) • Facilities costs – space, utilities (annual) • Labor to maintain & administer systems, migrate data (annual) • Disk: 3 FTE’s to administer disk storage & SAN • Archive: 3 FTE’s to administer archival systems • Annual costs normalized by: • Total SATA disk deployed (~1.8 PB SATA) • Current volume of data stored on tape (~5 PB) • Sustainable rate - $/TB/year • Assumed to be long-term storage w/ migration costs

8. Disk and tape storage cost elements • Media cost is not the • dominant cost (36%/20%) • Additional capital • infrastructure is • required (15%/33%) • Media + other capital • is ~half the total cost • (51%/53%) • Labor costs are a • significant cost (23%/20%) • Facilities costs modest • (11%/5%)

9. Disk/Tape Storage Cost Comparison: Relative Cost Elements

10. How do costs scale with the size of the storage infrastructure? • Economies of scale are significant as one moves up to “at-scale” installations ($/TB/yr decreases) • Vendor negotiations on media, other capital, maintenance • Fully utilizing servers, infrastructure and personnel • Once infrastructure is “at-scale”, economies of scale slow down and the cost ($/TB/yr) levels off with installation size • Media, supporting capital, maintenance, facilities costs • Perhaps some weak economies of scale in these factors • Some “linear” costs occur in large quantum steps – e.g. hiring additional administrator, larger servers to handle load • A portion of the cost elements (software licenses) are fixed with installation size => decreasing $/TB/yr for these elements • So with “at-scale” installations, net $/TB/yr will level off and then slowly decline

11. How will costs change in the future? • If annual costs decline exponentially with a halving time of Dt, the cost to store data in perpetuity is finite (1.44 * Dt * Current cost/yr) • Expect that exponential declines in media costs and other IT equipment will continue for a while • Cost ($/TB/yr) will decline, but how much? • Critical issue is which cost elements will scale with the declining media costs and which will not? • Most costs scale w/ media, but labor & facility costs may not scale well • Cost elements that do not scale well w/ media will dominate future costs, even at the ‘bit storage’ level • And we expect that for the broader ‘storage’ costs beyond bit storage, e.g. file management, labor costs will dominate! • New technologies • MAID for “disk archive”: capital cost comparable to disk, but lower operations costs (utilities, floor space) and extended useful lifetime • Disruptive storage technologies on horizon

12. What about trends in the relative cost of disk/tape storage? • Historical trends in media costs • Actual purchases over SDSC’s 20-year history indicate tape media cost/TB declines exponentially with halving time ~3 years • Apples-apples comparisons harder for disk, but halving time is shorter • If these trends continue, expect costs to converge within a few years • Even as costs converge, there may be good reasons to maintain a few large-scale centralized tape archives • Notion that there’s less risk to a tape cartridge than spinning disk

13. Comparison with Commercial Services • Many commercial companies are offering web-accessible storage services • One example - Amazon S3 (aws.amazon.com/s3) • Cost structure (~April 2007) - $1800/TB/yr storage + upload $100/TB + download $130-180/TB + put/get/list transaction fees • # of copies and media not specified, but speculate 2+ disk copies • Don’t know the capital/business model • No Guarantees - From AWS License Agreement “Amazon and its affiliates are not responsible for any unauthorized access to, alteration of, or the deletion, destruction, damage, loss or failure to store any Content or other data which you submit in connection with your account. “ SDSC cost estimates are “in the ballpark” w/ commercial services

14. Conclusions • Initial caveat … Bit storage costs are only a fraction of the total cost for ‘digital preservation’ • Ingest and use phases not addressed • Only a portion of storage phase costs included • SDSC’s sustainable single-copy ‘bit storage’ costs: • ~$500/TB/yr for tape storage • ~$1500/TB/yr for disk storage • Media costs are ~30% of the integrated ‘bit storage’ costs and total capital is ~50% of costs for both tape and disk • Costs ($/TB/yr) increase, then flatten out and eventually slowly decline w/ scale of installation • Costs will decline with time, but critical issue is which elements do not scale w/ media/technology advances • Disk/tape integrated costs are converging